Coated optical disks

ABSTRACT

Optical disks comprise a substrate, a metallized layer and a coating formed from a radiation-curable composition. The radiation-curable composition comprises a first component selected from the group consisting of alkanediol diacrylates, alkanediol dimethacrylates, alkene glycol diacrylates, alkene glycol dimethacrylates, and mixture thereof, and a second component comprising an acrylate- or methacrylate-containing alkoxylated bisphenol A compound. The compositions further include a photoinitiator and an adhesion promoter for promoting adhesion of the coating to the metallized substrate.

This application claims the benefit of Provisional application No.60/050,231 filed Jun. 19, 1997.

FIELD OF THE INVENTION

The present invention is directed to optical discs comprising asubstrate, a metallized layer and a coating, and more particularly tosuch optical discs wherein the coating is formed from aradiation-curable composition and has an advantageous combination ofphysical properties.

BACKGROUND OF THE INVENTION

Optical disk technology is well known in the art. Generally, in theformation of an optical storage disk such as a compact disk (CD), amolten transparent plastic is injection molded to form a substrate. Onone surface of the substrate, a replica of pits and lands contained inthe master mold is formed. A highly reflective layer of metal, forexample, gold, copper, silver or aluminum, is applied to the substratesurface which contains the pits and lands to allow the surface toreflect a laser beam of an optical disk reader such as a CD player. Thereflective layer is commonly made of aluminum and generally is appliedat a thickness of about 50 to 100 nanometers by vacuum deposition or thelike. Conventionally, the metallized substrate is then provided with anultraviolet (UV) curable coating by spin coating, electro-spraytechniques, vacuum deposition, or the like. Typically, when the coatingis applied by spin coating, a bead of a UV curable coating is applied tothe center inner diameter of the metallized substrate as the substrateis rotated to coat the entire surface. The coating is then cured and maybe subsequently printed if desired. Generally, the UV cured coatingprotects the metallized substrate from abrasion and humidity.

The Wolf et al U.S. Pat. No. 4,652,498 discloses an optical mediumcomprising a transparent substrate having an information-bearingsurface, a specularly reflective layer and a protective layer formedfrom a polymeric network of ethylenically unsaturated ingredients suchas polyacryloyl and polymethyacryloyl materials. A compound thatprovides phosphoric acid functionality is also included. The Namba et alU.S. Pat. No. 5,161,150 discloses optical recording discs having aprotective layer formed of a radiation-curable compound and aphoto-polymerization sensitizer. Suitable radiation-curable compoundsare disclosed as including oligo ester acrylates used in combinationwith radiation-curable monomers, examples of which include variousacrylates, diacrylates and triacrylates. The Dijkstra et al U.S. Pat.No. 4,188,433 discloses optical disks including a cover layer formedfrom an ultraviolet-curing lacquer containing a protic mixture ofacrylic acid esters. Epoxy acrylates and urethane acrylates are alsodisclosed as suitable.

Generally, conventional UV-curable coating compositions have providedoptical disks such as CD's with varying degrees of protection againstabrasion and humidity. It is also important that the cured coatingcomposition remains colorless and transparent, is easily printable andmay be produced at relatively low cost. Those skilled in the art willrecognize that not only are the UV coating composition's final physicalproperties important in providing an acceptable optical disk product,various properties of the uncured composition are also important. Forexample, the uncured composition must exhibit a low viscosity and goodflow to provide good, uniform coatings on the metallized substrate priorto cure. The cure speed of the coating composition is also important inproviding a product which may be readily mass produced. In manyconventional coating compositions, these desired features compete withone another so that improving one property, for example the viscosity ofthe uncured composition, disadvantageously effects another property, forexample the hardness of the cured composition. Accordingly, there is acontinuing need to develop coating compositions for optical disks whichoptimize these and additional, sometimes competing, requirements.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide opticaldisks which overcome disadvantages of the prior art. It is a morespecific object of the present invention to provide optical disks whichinclude a coating formed from a radiation-curable composition whichprovides an advantageous combination of properties. It is a furtherobject of the invention to provide optical storage disks such as compactdisks which exhibit an advantageous combination of physical properties.It is yet an additional object to provide optical disks which may beproduced at an improved rate as compared with conventional optical diskproducts.

These and additional objects are provided by the optical disks accordingto the present invention. More particularly, the disks comprise asubstrate, a metallized layer and a coating which is formed from aradiation-curable composition. In one embodiment, the radiation-curablecomposition comprises a first component selected from the groupconsisting of alkanediol diacrylates, alkanediol dimethacrylates, alkeneglycol diacrylates, alkene glycol dimethacrylates, and mixtures thereof,and a second component comprising an acrylate- ormethacrylate-containing alkoxylated bisphenol A compound. Theradiation-curable compositions further include a photoinitiator whichinitiates curing of the first and second components to form a hardprotective coating, and an adhesion promoter for promoting adhesion ofthe coating to the disk, for example to the metallized layer. Theadhesion promoter comprises acrylated sulfonic acid, methacrylatedsulfonic acid, acrylated sulfonic acid anhydride, methacrylated sulfonicacid anhydride, acrylated carboxylic acid, methacrylated carboxylicacid, acrylated carboxylic acid anhydride, methacrylated carboxylic acidanhydride, acrylated phosphoric acid, methacrylated phosphoric acid, ormixtures thereof.

The optical disks according to the present invention containing acoating formed from the described radiation-curable compositionsexhibits a good combination of physical properties, including goodhardness, good water resistance and good colorless transparency.Additionally, the radiation-curable compositions used to form thecoating in the optical disks of the present invention are easily appliedto fully and uniformly coat the metallized substrate and are quicklycured to facilitate mass production of the optical disks.

These and additional objects and advantages will be more fully apparentin view of the following detailed description.

DETAILED DESCRIPTION

The optical disks according to the present invention comprise asubstrate, a metallized layer and a coating. Typically, the substrate isformed by injection molding a transparent plastic in a mold, one side ofwhich mold contains a master stamper. In accordance with procedures wellknown in the compact disk manufacturing art, the master stamper may beformed with microscopic pits and lands which correspond with a recordedsignal, whereby one surface of the substrate resulting from theinjection molding contains a replica of the pits and lands contained onthe master. Typically, a center hole is punched out of the disksubstrate as the substrate is ejected from the molding machine. In oneembodiment, the transparent plastic which is used to form the discsubstrate comprises polycarbonate, various commercial forms of whichhave been specifically designed for use in producing compact disks andare readily commercially available.

The metallized layer is typically formed on the surface of the substratewhich contains the microscopic pits and lands, thereby rendering the pitand land-containing surface reflective to a light beam, for example alaser beam of the type in conventional CD players. The metallized layermay be formed of any suitable reflective metal. Gold, copper, silver andaluminum are preferred owing to their highly reflective properties, withaluminum being particularly preferred. The metallized layer is typicallyformed by vacuum deposition, although other techniques known in the artmay be employed, and at a thickness of about 50 to 100 nanometers,although the thickness may vary depending on the specific intended useof the disk.

The optical disc coating is formed from a radiation-curable compositionand preferably is formed on the metallized layer. The radiation-curablecomposition from which the coating is formed comprises a first componentselected from the group consisting of alkenediol diacrylates, alkenedioldimethacrylates, alkeneglycol diacrylates, alkeneglycol dimethacrylatesand mixtures thereof, and a second component comprising an acrylate ormethacrylate-containing alkoxylated bisphenol A compound. Thesecomponents, together with the photoinitiator and adhesion promotercombine to provide compositions which cure quickly to form uniformcoatings having good hardness and water resistance. The cured coatingcompositions are transparent and colorless, further contributing totheir advantageous use in the optical disks of the present invention.

The alkane and/or alkene moiety of the first component included in theradiation-curable compositions preferably has from about 2 to about 10carbon atoms, or may comprise a polymeric moiety having a repeating unitcontaining from about 2 to about 10 carbon atoms. Examples of the firstcomponent suitable for use in the radiation-curable compositionsinclude, but are not limited to, 1,3-propanediol diacrylate ordimethacrylate, 1,4-butanediol diacrylate or dimethacrylate,1,6-hexanediol diacrylate or dimethacrylate, diethylene glycoldiacrylate or dimethacrylate, triethylene glycol diacrylate ordimethacrylate, polyethylene glycol diacrylate or dimethacrylate,tripropylene glycol diacrylate or dimethacrylate, and the like.Generally, this component contributes to the low viscosity of theradiation-curable compositions from which the optical disk coating isformed and contributes to the continuous and uniform coverage which thecoating provides on the metallized substrate. In a preferred embodiment,the first component comprises 1,6-hexanediol diacrylate, alone or incombination with an additional alkanediol diacrylate, alkanedioldimethacrylate, alkeneglycol diacrylate or alkenediol dimethacrylate.

The second component included in the radiation-curable compositions fromwhich the optical disk coatings are formed comprises a compoundgenerally of the formula:

R¹—X¹—Z—X²—R²

wherein each of R¹ and R² is individually a radiation-curable functionalgroup, each of X¹ and X² is individually an alkyleneoxy group havingfrom about 2 to about 40 carbon atoms and includes an oxygen atomlinkage to Z, and Z is a hydrocarbon group having from about 5 to about40 carbon atoms and contains at least one cyclic group. The secondcomponent contributes to the fast curing of the radiation-curablecompositions and contributes to the good hardness of the optical diskcoating. In a particularly preferred embodiment, the second componentcomprises ethoxylated bisphenol A diacrylate.

The amounts of the first and second components included in theradiation-curable compositions may vary in order to optimize theproperties of a particular combination of components, for example tooptimize the viscosity and cure speed of the compositions and thehardness, water resistance and colorless transparency of cured coatingsformed therefrom. In this regard, it is preferred that the viscosity ofthe radiation-curable composition is in the range of from about 10 toabout 200 cps, more preferably from about 30 to about 70 cps, asmeasured according to ASTM-D-2196. In a further preferred embodiment,the radiation-curable composition can be effectively cured usingultraviolet light at a level of about 300 mJ/cm² in less than about 2seconds, and more preferably in less than about 1 second. Once theradiation-curable compositions are applied to the metallized substrateand cured, it is preferred that the resulting coating exhibits a pencilhardness of at least B, and more preferably of at least HB, as measuredaccording to ASTM-D-3363-74. It is also preferred that the curedcompositions, which are transparent and colorless, i.e., non-yellowing,exhibit APHA color of from about 0 to about 100, as measured accordingto ASTM-D-1209.

Preferably, the radiation-curable compositions comprise from about 20 toabout 70 weight percent of the first component and from about 20 toabout 70 weight percent of the second component. More preferably, theradiation-curable compositions comprise from about 30 to about 60 weightpercent of the first component and from about 30 to about 60 weightpercent of the second component in order that the compositions and thecured coatings produced therefrom have an advantageous combination ofthe aforementioned properties.

In a further embodiment of the invention, the radiation-curablecompositions may include one or more additional reactive acrylatecomponents, for example acrylates or methacrylates containing polyols,or compounds derived therefrom, and/or urethane acrylates ormethacrylates. Acrylate and methacrylate oligomers of this type whichare UV curable are well known in the art and commercially available andinclude, for example, trimethylol propane triacrylates,pentaerythritol-containing acrylates such as pentaerythritoltetracrylate, neopentyl glycol (PO) diacrylate and dipentaerythritolmonohydroxy pentacrylate, di-trimethyolpropane tetracrylate, and thelike. Urethane acrylate components are also suitable for use as theadditional reactive acrylate component, including isocyanurate mono-,di- or tri-acrylate components, or mixtures thereof. When theradiation-curable compositions include at least one additional reactiveacrylate component in combination with the first and second components,the content of one or both of the first and second components can bereduced. In a preferred embodiment in which an additional reactiveacrylate component is employed, the compositions comprise from about 20to about 70 weight percent of the first component, from about 5 to about40 weight percent of the second component and from about 10 to about 50weight percent of the additional reactive acrylate component orcomponents. More preferably, these radiation-curable compositionscomprise from about 30 to about 60 weight percent of the firstcomponent, from about 10 to about 30 weight percent of the secondcomponent, and from about 20 to about 40 weight percent of theadditional reactive acrylate component or components.

The radiation-curable compositions further include a photoinitiator inorder to initiate curing of the compositions, particularly the first andsecond components, in response to radiation exposure. The compositionsaccording to the present invention are advantageously UV curable.Various photoinitiators are known in the art and may be employed in theradiation-curable compositions of the present invention. Examples ofphotoinitiators suitable for use in the compositions of the presentinvention include, but are not limited to, benzoin or alkyl ethersthereof such as the benzophenones, phenyl methyl ketone (acetophenone),substituted acetophenones, anthraquinones, polynuclearquinones,disulfides or benzil. In a preferred embodiment, the photoinitiatorcomprises benzophenone, an acetophenone, substituted or unsubstituted,or a mixture thereof, and more preferably comprises a substitutedacetophenone. The photoinitiator is included in the radiation-curablecompositions in an amount sufficient to initiate curing of the first andsecond components. Preferably, the photoinitiator is included in anamount of from about 2 to about 15 weight percent of the composition andmore preferably in an amount of from about 5 to about 12 weight percentof the composition, and further preferable in an amount of from about 8to about 10 weight percent of the composition.

The radiation-curable compositions from which the optical disk coatingsare formed further include an adhesion promoter for promoting adhesionof the coating to the disk, particularly the metallized substrate of theoptical disk. As a result, the optical disks of the invention exhibitimproved coating properties, thereby increasing the durability of theoptical disks. Generally, the adhesion promoter comprises anorganofunctional acidic compound. Preferably, the adhesion promotercomprises acrylated sulfonic acid, methacrylated sulfonic acid,acrylated sulfonic acid anhydride, methacrylated sulfonic acidanhydride, acrylated carboxylic acid, methacrylated carboxylic acid,acrylated carboxylic acid anhydride, methacrylated carboxylic acidanhydride, acrylated phosphoric acid, methacrylated phosphoric acid, ormixtures thereof. The acrylate or methacrylate moiety of the adhesionpromoter is believed to increase the compatibility of the adhesionpromoter with the first and second components. The adhesion promoter isincluded in the radiation-curable compositions in an amount sufficientto improve adhesion of the cured compositions to the adjacent layer ofthe optical disk, commonly the metallized substrate. In a preferredembodiment, the adhesion promoter is included in an amount of from about0.01 weight percent to about 1 weight percent of the radiation curablecomposition. More preferably, the adhesion promoter is included in anamount of from about 0.05 weight percent to about 0.5 weight percent,and further preferable in an amount of from about 0.05 weight percent toabout 0.3 weight percent of the curable composition. In a furtherpreferred embodiment, the adhesion promoter comprises an acrylatedphosphoric acid or a methacrylated phosphoric acid, or a mixturethereof.

The radiation-curable compositions from which the optical disk coatingsare formed may further include one or more conventional additives whichdo not materially effect the optimal combination of properties providedby the aforementioned essential components. For example, thecompositions may optionally include a flow promoter in order to promotethe radiation curable compositions' ability to quickly, completely anduniformly coat a metallized substrate to which the composition isapplied. Suitable flow promoters comprise reactive silicone acrylate andmethacrylate compounds, high molecular weight acrylic compounds and thelike which are commercially available. Any such flow promoter, ifincluded, is employed in a relatively low amount so as not todisadvantageously effect the optimal combination of physical propertiesof the radiation-curable coating compositions and the cured coatingsformed therefrom. In a preferred embodiment, a flow promoter is includedin the radiation-curable compositions in an amount of up to about 0.5 byweight percent of the composition, and more preferably in an amount offrom about 0.01 to about 0.3 weight percent.

The radiation-curable compositions are prepared using conventionalprocessing techniques. Generally, if any of the acrylate or methacrylatecomponents are in a solid form, they are liquefied by heating and thenmixed together with the remaining components. The resulting liquidmixture may be filtered if necessary, for example through a 0.45 umfilter or the like, before application to the metallized substrate. Theradiation-curable compositions may be applied to the metallizedsubstrate in accordance with any of the techniques well known in theart. For example, the radiation-curable compositions may be appliedusing spin coating techniques, electro-spray techniques or vacuumdeposition. Preferably and conventionally, the radiation-curablecompositions are applied to the metallized substrate using spin coatingtechniques known in the art. The compositions according to the presentinvention are advantageously of a viscosity which allows spin coatingtechniques to be used to apply the compositions and obtain thorough,uniform coating on the disks, commonly on the metallized substrate.

In accordance with conventional techniques, the composition may beapplied to the disk using a syringe, preferably including an in-linefilter. After application of the composition, the disk is spun todistribute the composition across the surface of the disk in a thoroughand uniform manner. The coated disk may then be exposed to radiation tocure the composition and form a hard protective coating. The uncuredcomposition of the present invention may be cured using any suitableform of radiation, for example electron beam radiation or ultravioletradiation. It is preferred that the composition be photocurable, i.e.,curable with ultraviolet radiation. Various sources of UV radiation aresuitable, including, but not limited to, electric powered arc lamps,such as medium pressure or high pressure mercury lamps, andelectrodeless lamps such as H-type, D-type or V-type metal halide lamps.As an example, a UV radiation source operating at wave lengths of fromabout 240 to about 450 nm and an energy of from about 200 to about 450mJ/cm² is suitable. Once the radiation-curable compositions are cured,the resulting coating may be printed on with ink as desired. Thecoatings according to the present invention formed from theradiation-curable compositions as described suitably accept ink printingthereon.

The detailed description of the optical disks of the present inventionhas indicated that typically the disks are of the CD type. Also withinthe scope of the present invention are optical discs, inter alia, of theCD-R, CD-ROM and DVD formats.

The optical disks according to the present invention are furtherdemonstrated by the following Example. In the Example, and throughoutthe present specification, all parts and percentages are by weight,unless otherwise specified.

EXAMPLE

With reference to Table I, radiation-curable compositions were preparedfrom the indicated components using the recited weight percentages:

TABLE I Radiation Curable Compositions Component, wt. % A B1,6-Hexanediol diacrylate 46.75 40.75 Ethoxylated bisphenol A diacrylate13.00 50.00 Tris(2-hydroxyethyl)isocyanurate 31.00 — triacrylateIrgacure 184¹ 9.00 9.00 Ebecryl 168² 0.15 0.15 Silicone acrylate flowpromoter 0.10 0.10 ¹Photoinitiator comprising 1-hydroxycyclohexyl phenylketone ²Adhesion promoter comprising carboxylic/phosphoric acidmethacrylate

In preparing composition A identified above, the isocyanuratetriacrylate component was first heated for 24 hours at about 65° C. tomelt the component and facilitate its use. The components of eachcomposition A and B were added to a blend tank in the order set forth inTable 1. Shear was then initiated and the temperature of the blend tankwas raised to about 56° C. The compositions were maintained under theseconditions for approximately one hour, and were then filtered through a0.45 micron filter in preparation for application to optical diskmetallized substrates. Compositions A and B were measured as exhibitingviscosities of 52.4 cps and 63.5 cps according to ASTM-D2196. Thecompositions were cured at 300 mJ/cm² and determined to exhibit a pencilhardness of B and HB, respectively, according to pencil hardness testASTM-D3363-74. Thus, the compositions and the cured products producedtherefrom exhibited an advantageous combination of properties.

This example is set forth to illustrate a specific embodiment of theinvention and is not intended to be limiting thereof. Additionalembodiments and advantages of the present invention will be apparent toone of ordinary skill in the art.

What is claimed is:
 1. An optical disc, comprising a substrate, ametallized layer and a coating, the coating being formed from aradiation-curable composition comprising from about 30 to about 70weight percent of a first component selected from the group consistingof alkanediol diacrylates, alkanediol dimethacrylates, alkene glycoldiacrylates, alkene glycol dimethacrylates, and mixtures thereof, fromabout 20 to about 70 weight percent of an acrylate- ormethacrylate-containing alkoxylated bisphenol A compound as a secondcomponent, a photoinitiator and from about 0.01 to about 1 weightpercent of an adhesion promoter for promoting adhesion of the coating tothe disc, the adhesion promoter comprising acrylated sulfonic acid,methacrylated sulfonic acid, acrylated sulfonic acid anhydride,methacrylated sulfonic acid anhydride, acrylated carboxylic acidmethacrylated carboxylic acid, acrylated carboxylic acid anhydride,methacrylated carboxylic acid anhydride, acrylated phosphoric acid,methacrylated phosphoric acid, or mixtures thereof.
 2. An optical discas defined by claim 1, wherein the radiation curable compositioncomprises from about 2 to about 15 weight percent of the photoinitiator.3. An optical disc as defined by claim 1, wherein the radiation curablecomposition comprises from about 30 to about 60 weight percent of thefirst component, from about 30 to about 60 weight percent of the secondcomponent, from about 5 to about 12 weight percent of the photoinitiatorand from about 0.05 to about 0.5 weight percent of the adhesionpromoter.
 4. An optical disc as defined by claim 1, wherein the firstcomponent comprises an alkanediol diacrylate.
 5. An optical disc asdefined by claim 1, wherein the first component comprises hexanedioldiacrylate.
 6. An optical disc as defined by claim 1, wherein the secondcomponent comprises ethoxylated bisphenol A diacrylate.
 7. An opticaldisc as defined by claim 1, wherein the radiation curable compositionfurther comprises at least one additional reactive acrylate component.8. An optical disc as defined by claim 7, wherein the additionalreactive acrylate component comprises ethoxylated triacrylate,pentaerythritol polyacrylate, isocyanurate mono-, di-, or triacrylate,or mixtures thereof.
 9. An optical disc as defined by claim 1, whereinthe adhesion promoter comprises an acrylated phosphoric acid or amethacrylated phosphoric acid, or a mixture thereof.
 10. An optical discas defined by claim 1, wherein the radiation curable composition furthercomprises a flow promoter.
 11. An optical disc as defined by claim 10,wherein the flow promoter comprises a reactive silicone (meth)acrylatecompound or a high molecular weight acrylic compound and is included inan amount of from about 0.01 to about 0.5 weight percent.
 12. An opticaldisc as defined by claim 1, wherein the photoinitiator comprises abenzophenone, an acetophenone, or a mixture thereof.
 13. An optical discas defined by claim 1, wherein the substrate is formed of polycarbonate.14. An optical disc as defined by claim 1, wherein the coating is formedon the outer surface of the disc.
 15. An optical disc as defined byclaim 14, wherein the coating is cured and is provided with inkprinting.
 16. An optical disc as defined by claim 1, wherein thesubstrate is formed with pits and lands and the optical disc is anoptical storage disc.
 17. An optical disc as defined by claim 1, whereinthe radiation-curable composition from which the coating is formed has aviscosity of from about 10 to about 200 cps and is effectively curableusing an ultraviolet radiation source operating at a wavelength of fromabout 240 to about 450 nm and an energy of from about 200 to about 450mJ/cm² in less than about 2 seconds to provide a cured coating having apencil hardness of at least B.
 18. An optical disc as defined by claim1, wherein the radiation-curable composition from which the coating isformed has a viscosity of from about 10 to about 200 cps and iseffectively curable using an ultraviolet radiation source operating at awavelength of from about 240 to about 450 nm and an energy of from about200 to about 450 mJ/cm² in less than about 2 seconds.
 19. An opticaldisc as defined by claim 1, wherein the radiation-curable compositioncomprises from about 30 to about 70 weight percent of the secondcomponent.
 20. An optical disc as defined by claim 1, wherein theradiation-curable composition comprises from about 30 to about 60 weightpercent of the second component.
 21. An optical disk, comprising asubstrate, a metallized layer and a coating, the coating being formedfrom a radiation-curable composition comprising from about 30 to about70 weight percent of a first component selected from the groupconsisting of alkanediol diacrylates, alkanediol dimethacrylates, alkeneglycol diacrylates, alkene glycol dimethacrylates, and mixtures thereof,from about 5 to about 40 weight percent of an acrylate- ormethacrylate-containing alkoxylated bisphenol A compound as a secondcomponent, from about 10 to about 50 weight percent of an additionalreactive acrylate component comprising ethoxylated triacrylate,pentaerythritol polyacrylate, isocyanurate mono, di- or triacrylate, ora mixture thereof, from about 2 to about 15 weight percent of aphotoinitiator, and from about 0.01 to about 1 weight percent of anadhesion promoter comprising acrylated sulfonic acid, methacrylatedsulfonic acid, acrylated sulfonic acid anhydride, methacrylated sulfonicacid anhydride, acrylated carboxylic, methacrylated carboxylic acid,acrylated carboxylic acid anhydride, methacrylated carboxylic acidanhydride, acrylated phosphoric acid, methacrylated phosphoric acid, ormixtures thereof.
 22. An optical disc as defined by claim 21, whereinthe radiation curable composition comprises from about 30 to about 60weight percent of the first component, from about 10 to about 30 weightpercent of the second component, from about 20 to about 40 weightpercent of the additional reactive acrylate component, from about 5 toabout 12 weight percent of the photoinitiator and from about 0.05 toabout 0.5 weight percent of the adhesion promoter.
 23. An optical discas defined by claim 1, wherein the radiation-curable compositioncomprises from about 20 to about 50 weight percent of the additionalreactive acrylate component.
 24. An optical disc as defined by claim 21,wherein the radiation-curable composition comprises from about 20 toabout 40 weight percent of the additional reactive acrylate component.